1. Field of the Invention
The present invention relates to piston-type compressors for use in vehicular air conditioning systems. More particularly, it relates to cylinder bores and pistons that reciprocate within cylinder bores.
2. Description of Related Art
Piston-type compressors are known in the art. For example, Japanese Second (Examined) Utility Model Publication No. 452473 discloses a piston-type compressor. Such piston-type compressors have pistons, which reciprocate in cylinder bores. A groove is formed on an outer peripheral surface and at about a first end of the piston. A piston ring, which is a truncated cone-shaped ring and may be made of resin, is fitted into the groove formed around the outer peripheral surface of the piston. The piston ring increases the sealing efficiency during compressor operation, and thereby increases the efficiency of compressor operation.
In such piston-type compressors, because compressed gas is drawn into a space between the groove of the outer peripheral surface of the piston and an interior surface of the piston ring, the sealing efficiency between the piston and the cylinder bore is increased. On the other hand, lubricating oil included in blow-by gas is largely prevented from seeping into a crank chamber. Consequently, it is difficult to maintain lubricating oil in the crank chamber, and lubrication of components within the crank chamber may be reduced.
A piston-type compressor which maintains lubricating oil in the crank chamber is described in U.S. patent application Ser. No. 09729,321, which is incorporated herein by reference. This piston-type compressor comprises a plurality of cylinder bores and pistons, which reciprocate in cylinder bores. A piston ring, which is a truncated cone-shaped ring and may be made of resin, is fitted into the groove formed around the outer peripheral surface of the piston. An eternal diameter of the piston ring is greater than that of the piston. The piston ring is disposed in the groove, such that the wider edge of the piston ring opens toward a piston skirt portion of the piston and the narrower edge of the piston zing abuts the bottom surface of the groove. In this piston-type compressor, the piston ring is disposed in the groove of the piston, such that the wider edge of the piston ring opens toward the piston skirt portion of the piston, and only the narrower edge of the piston ring adheres to the bottom surface of the groove of the piston. Therefore, during compressor operation, the sealing efficiency of sliding members between the pistons and cylinders maintains high efficiency, and blow-by gas leaks into a crank chamber from cylinder bores at the same time. As a result, the retention of lubricating oil included in blow-by gas in the crank chamber may increase, and lubricating efficiency of sliding members in the crank chamber may increase.
A need has arisen to provide a compressor which has sufficient sealing efficiency for sliding portions between a piston and a cylinder bore, as well as which maintains sufficient lubricating oil within a crank chamber by leaking blow-by gas into the crank chamber from the cylinder bore in compressor operation.
A further need has arisen for a compressor which prevents the build-up of excess amounts of lubricating oil in the crank chamber. It is an advantage of such compressors that rubber gaskets, such as sealing members for the drive shaft at entry and exit points in the crank chamber, are not adversely effected by prolonged exposure to lubricating oil.
In an embodiment of this invention, a compressor comprises a plurality of cylinder bores and a plurality of piston assemblies. Each piston assembly reciprocates between a top dead center and a bottom dead center position one of the cylinder bores. The piston assembly comprises a piston having a first groove, which is formed on an outer peripheral surface and at about a first end of the piston. A piston ring having a truncated cone-shape is insured into the first groove, such that a wider edge of the piston ring opens toward a piston skirt portion of the piston and a narrower edge of the piston ring abuts a bottom surface of the first groove. A second groove is formed on an interior wall of at least one of the cylinder bores, and extends along an axial line between a crank-chamber-side end of the cylinder bore and about an end of bottom dead center position.
Objects, features, and advantages will be apparent to persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings.